Postoperative Olfaction Alteration Following Laparoscopic Bariatric Surgery

The Role of the Olfactory System in Obesity and Metabolism in Humans: A Systematic Review and Meta-Analysis

Obesity, linked to chronic diseases, poses a global health challenge. While the role of the olfactory system in energy homeostasis is well-documented in rodents, its role in metabolism regulation and obesity in humans remains understudied. This review examines the interplay between olfactory function and metabolic alterations in human obesity and the effects of bariatric surgery on olfactory capabilities in humans. Adhering to PRISMA guidelines, a systematic review and meta-analysis was conducted, focusing exclusively on original human studies. From 51 articles, 14 were selected for the meta-analysis. It was found that variations in olfactory receptor genes influence the susceptibility to odors and predisposition to weight gain and poor eating habits. Bariatric surgery, particularly sleeve gastrectomy, shows significant improvements in olfactory function (SMD 2.37, 95% CI [0.96, 3.77], I = 92%, p = 0.001), especially regarding the olfactory threshold (SMD -1.65, 95% CI [-3.03, -0.27], I = 81%, p = 0.02). There is a bidirectional relationship between olfactory function and metabolism in humans. Bariatric surgery improves olfactory perception in obese patients, but it is still unclear if impacting the olfactory system directly affects eating behavior and the energy balance. However, these findings open novel avenues for future studies addressing the olfactory system as a novel target to alter systemic metabolism in humans.

Olfaction in the context of obesity and diabetes: Insights from animal models to humans

The olfactory system is at the crossroad between sensory processing and metabolic sensing. In addition to being the center of detection and identification of food odors, it is a sensor for most of the hormones and nutrients responsible for feeding behavior regulation. The consequences of modifications in body homeostasis, nutrient overload and alteration of this brain network in the pathological condition of food-induced obesity and type 2 diabetes are still not elucidated. The aim of this review was first to use both humans and animal studies to report on the current knowledge of the consequences of obesity and type 2 diabetes on odorant threshold and olfactory perception including identification discrimination and memory. We then discuss how olfactory processing can be modified by an alteration of the metabolic homeostasis of the organism and available elements on pharmacological treatments that regulate olfaction. We focus on data within the olfactory system but also on the interactions between the olfactory system and other brain networks impacted by metabolic diseases.

Olfactory and Gustatory Function before and after Laparoscopic Sleeve Gastrectomy

Background and Objectives: Bariatric surgery is the gold standard for the treatment of morbid obesity, and current evidence suggests that patients undergoing surgery can show changes in their sense of taste and smell. However, no definitive conclusions can be drawn given the heterogeneity of the studies and the contrasting results reported in the literature. Materials and Methods: We enrolled 18 obese patients undergoing laparoscopic sleeve gastrectomy (LSG) and 15 obese controls. At baseline (T0) and 6 months after enrollment/surgery (T1), both groups underwent Sniffin’ Sticks and whole mouth test. Post-operative qualitative taste variations were also analyzed and SNOT-22, VAS for taste and smell, and MMSE were administered. Results: An improvement in the olfactory threshold was observed in the treatment group (p = 0.03) at 6 months. At multivariate analysis, the olfactory threshold differences observed correlated with MMSE (p = 0.03) and T0 gustatory identification (p = 0.01). No changes in sense of taste were observed between the two groups at 6 months, even though nine subjects in the treatment group reported a worsening of taste. This negatively correlated with age (p < 0.001), but a positive marginal correlation was observed with the olfactory threshold difference between T0 and T1 (p = 0.06). Conclusions: Olfaction can improve after LSG, and this seems to be the consequence of an improved olfactory threshold. Although we did not observe any change in gustatory identification, food’s pleasantness worsened after bariatric surgery.